1. Field of the Invention
The present invention relates to a combined generating plant constituted by combining a gas turbine and a steam turbine and its start-up control device and start-up control method.
2. Discussion of the Background
In general, in a combined cycle generating plant constituted by combining a gas turbine and a steam turbine, the hot gas that is discharged by the gas turbine after doing work is utilized to generate steam by heat exchange with water using a waste heat recovery boiler. This steam is then used to generate electricity by driving a steam turbine, thereby achieving more effective utilization of the heat energy.
One example of a combined cycle generating plant of this kind is a single-shaft combined cycle generating plant, as shown in FIG. 1. In this single-shaft combined cycle generating plant, a gas turbine 100 consisting of a compressor 101, a burner 102, and an expansion turbine 103, a generator 104, and a steam turbine 105 consisting of a high-pressure turbine 105a and a low-pressure turbine 105b are linked by a series of rotary shafts in skewer fashion. A start-up device 107 is coupled to one end of this rotary shaft, on the same side as compressor 101, through a torque converter 108.
In this construction, atmospheric air flows into and is compressed by compressor 101 so that liquid or gaseous fuel 109 can be burnt with it in burner 102, producing hot gas. The flow of fuel 109 is regulated by a fuel control value 118. Then, after performing work in expansion turbine 103, it is fed to a waste heat recovery boiler 111 of a steam generator 200 by a discharge duct. Steam generator 200 is provided with waste heat recovery boiler 111, high-pressure drum 112 and low-pressure drum 113. Waste heat recovery boiler 111 performs heat exchange with the hot waste gas from gas turbine 100, so that high-pressure steam is generated by high-pressure drum 112 and low-pressure steam is generated by low-pressure drum 113. The high-pressure steam generated in high-pressure drum 112 flows into high-pressure turbine 105a through main steam stop valve 115 of main steam pipe 114 and steam regulating valve 116.
In contrast, the low-pressure steam generated by low-pressure drum 113 is merged with the steam discharged from high-pressure turbine 105a and flows into low-pressure turbine 105b through low-pressure steam stop valve 118 of low-pressure steam pipe 117 and low-pressure steam regulating valve 119. After the steam has done work in low-pressure turbine 105b, it flows into a condenser 106, where it is condensed to form condensate which is returned to waste heat recovery boiler 111 by a water feed pump 120.
Main steam pipe 114 is provided with a high-pressure bypass pipe 121, whereby excess steam is transferred to condenser 106 through high-pressure bypass valve 122. Likewise low-pressure steam pipe 117 is provided with a low-pressure bypass pipe 123 whereby excess steam is transferred to condenser 106 through low-pressure bypass valve 124.
In start-up of the combined cycle generating plant, first gas turbine 100 must first be started. Start-up device 107 is provided for this purpose. The driving force of this start-up device 107 is transmitted to gas turbine 100 through torque converter 108.
The reason for this is that, in starting up gas turbine 100, air must be compressed by compressor 101, but compressor 101 does not operate unless gas turbine 100 is rotating. Start-up device 107 in therefore used to raise the speed of rotation of gas turbine 100 usually until it reaches about 60% of its rated speed. Compressor 101 is then actuated so that high-pressure turbine 103 is operated independently by means of hot gas generated by ignition of burner 102. Once gas turbine 100 is operating independently, start-up device 107 is no longer needed.
Thus, in start-up of a combined cycle generating plant, a start-up device 107 is required to start gas turbine 100.
However, with an increase in the capacity of gas turbine 100, the capacity of start-up device 107 must also be increased. Thus start-up device 107 becomes large in size and needs a high-power power source. Torque converter 108 also becomes large in capacity, resulting in increased size of the equipment and higher costs.